Trigger circuit



, u P ITU A TRAMSLAT NG Fan D. D. GRIEG TRIGGER CIRCUIT Filed Sept.5,-1'942 ()RCUIT AMPLIFIER Feb. 25, 1947.

INVENTOR Y DONALD 0. GR/EG Arr RNEYI- Patented Feb. 25, 1947 TRIGGERCIRCUIT. I I, DonaldD. Grieg-, Forest Hills, Yaeassi'glnor:

Federal Telephone and Badiosflorporation az corporationof Delaware yApplication September 5, 942; Serial-No: 457,396 (o1 zeal-e247 6 Claims.

This: invention relates to radio'frequency circuits: and moreparticularly to trigger circuits to be-controll'edby received radiofrequency pulses.

For the purpose of economy in power and for preservation of, a modicumof 'secrecy, transmission of energy by time modulated impulses is oftenresorted to. This type of' system is quite fully: set forth in UnitedStates patents. to A. Reeves, Nosi 2266,40]. and 2256336 and in UnitedStates-patent-to Edmond M. Deloraine and A. ReevesNo. 2,262,383.

A particularly valuabletype of such systems from the standpoint ofavoiding interception is that described in: the copendi'ng applicationsof Edmond M. Deloraineand Emile Labin, entitled "Pulse transmissionsystem," Serial No. 425,108,

derived: from the input pulses; to a. circuit tuned to: indifferent:radio; frequency harmonically re.- lated. to the; pulse; envelope, a:series of output pulsesof a difierentcarrier radio frequency and thevsame: relative time; spacings which; may be readily detected by known.means or used. for

' other: purposes: may be obtained:

filed December 31, 1941 and Emile'Labin, en-

titled Radio receiverfiSerial No. 449,595, filed July 3, 1942;

' In the last named application is described a system wherein receivedpulsesare amplified, detected and limited, after'whi'ch they are appliedto a trigger circuit; The shaping circuit serves to give to the detectedpulses a fixed duration independent of the duration of thereceivedpulse.

cation; are applied over a resonant" circuit to the input 'oi'atranslating circuit. This tri'gger circuit'is preferably i'nthe form-ofa multi'-vibratorwith a fixed time constant of operation. The leadingedge of an-i'ncomingradio irequency 'pul'se serves to operate thetrigger circuit: and it remains/ int operation for a definite per-iodindeependentof the'l'ength oi the applied pulse. The

time period f'orwhi'ch thetrigger circuit remains operated is greaterthan the duration of the -applied' radio frequency pulse and therefore:producesa pulse in the output which hasa spacing; in time; dependentupon the applied radio: free quency 'pulsebut a duration independentthereof; The trigger circuitmay also servet'o produce pulses of anamplitude independent of'thel applied'radio frequency pulses. e l

By applying the envelope direjct -currentpulses A; better understanding"of my invention and the objectsandvfeaturesthereof' maybe had: from theparticular description: of: an embodiment. of my inventionmade=withvreferenceto the acconrpanyin'g drawings in: whichz'.

Fig; 1 is' a? block di-agramaofj a receiver-incur porating: myinvention;

Fig. 2 is: asset:- of curves: used in explaining theicperati'on of myinvention;

Fig; 3 islthe' circuit diagram of' a: trigger circult in accordance withmyrinvention and Fig.4 shows an additional output element which may beused with-.the trigger" circuit of Fig; 3., In Fig. 1= is showndiagrammatically a time modulated impulse receiving system incorporating my invention. This receiver includes the usual-antenna H3 andthelradio frequency ame plifier H which. may also serve to reduce thereceived radio frequencysignals to a common intermediate frequency.This" intermediate frequenc'y preferablyalso is in: the radio frequencyrange; If the system is to be used for reception of impulses fromstations: transmitting at-dif ferent' frequencies, it is desirable thatthe received 'irequencies be; reduced to the sameinter cor-din gl'y;the-impulses in the output; of the-trig gercircuit will be in theformof' direct current impulses with allof the radio frequency carrierremoved therefrom. Noseparate envelopede-' t'ector circuitandtriggercircuit is necessary as irrprevious circuits cit-his type. 5

Theoutput' signals from-trigger circuit i2 are then" applied to adetector I3 overa band pa'ss filter l 4 preferably: after being limitedin' lime itei 55f If" the pulses are.- amplitudea medulated as; well:times: mcdulated, the signals; ire, the outputiof-i amplifier: l lamentbe applied to; another;

stead of a single tube structure.

detector l6 for deriving the amplitude modulated signal.

It will be recognized that the receiver circuit of Fig. 1 performssubstantially the same function as the prior art system outlined above.The circuit according to my invention, however, does not require thedetecting circuit for the 'pulses prior to application thereof to thetrigger circuit. Likewise, the input limiter is unnecessary in thiscircuit in accordance with my invention as will be more clearly broughtout in the specific description of the shaping circuit.

The trigger circuit which constitutes thejprincipal feature of myinvention will now be described with reference to Figs. 2 and 3. Theradio frequency impulses in the output of amplifier II will be in theform shown in curve A of Fig. 2.

The two pulses 20 and 2| which define one pair of time-modulated:impulses are each composed of a high frequency carrier wave as shown.Although only a relatively small number of oscillations are shown in thefigure, the actual number of oscillations in each pulse may be fairlyhigh. For example, if the entire pulse duration Y r is two microsecondsand an intermediate frequency of 50 megacycles is used, there will be100 oscillations during one pulse. With higher frequencies there will bea correspondingly larger number of oscillations per pulse. The pairs ofpulses in the received series, 20, 2| and 22, 23 are separated by arelatively fixed period T.

The pulses of this received series are applied preferably to the tunedprimary 30 (Fig. 3) of thetuned input circuit 3| of trigger circuit l2.This triggercircuit comprises a vacuum tube device 7 32 operating as amultivibrator or trigger circuit.

A common envelope with two sets of electrodes is shown but it should beunderstood that separate vacuum tubes may be used if desired in- Thismultivibrator circuit has two setsof electrodes, cathode 40, grid 4| andanode 42, and cathode 50, grid 5| and anode 52. The cathodes 40 and 50are interconnected and coupled to ground through an adjustable resistordevice 35. This adjustable resistor serves as a common'resistance in theanode-cathode circuit'of both sets-of electrodes and provides thefeedback necessary for operation of the arrangement as a multi-vibrator.In the absence of a signal, grid 5| is maintained negative by means of abias source-53 so that the corresponding set of electrodes is normallynoneconductive. The energy flowing through the first section of thistube and through resistance 35 maintains 'grid 4| slightly negative inthe normal condition. Grid 5| also tends to become more negative addingto the negative bias. Upon application of a predetermined negativevoltage to grid 4| the electrode system 40, 4| and 42 provides anamplification of this voltage. This operation then swingsgrid 5| in apositive direction by reason of the drop through resistance 58 and thecharge on condenser 55 overcoming the effect of the negative bias onthis grid. Simultaneously, the electrode system 40, 4|, 42 is drivenfurther negatively to cut-off by virtue of the feedback voltage acrossresistance 35. A0-

trodes 50 and 52 and the current between electrodes 40 and 42 commences.The duration of this operative condition of the multi-vibrator triggermeans is determined by the adjustment of resistance 35 and the timeconstant of resistances 56 and 59, condenser 55 and anode load 55, thetube would remain inoperation.

' initiating cordingly, an. output signal is initiated in the Vmulti-vib-rator trigger circuit across resistance 51.. If the negativevoltage applied to the grid does not continue the chargeon condenser 55associated with grid 5| willleak ofi through resistance 56. As soon asthis charge .has been reduced so that this section of thetube is again 7cutoff by the bias, currentceases between elecsufficient potential toinitiate operation of tube electrodes 40, 4| and 42. This developedpotential is applied to the input over resistance 59 and couplingcondensers 68, 6|. A decoupling resistance 52 of high value is arrangedconnected between tuned circuit 3| and ground. Normally, it will take anumber of applied oscillations to cause this operation but this numberwill be relatively small compared to the .total numberin the pulse. Eachnegative swing of a received wave train pulse adds to the effect tendingto make grid 4| negative. After operation of the trigger circuit,however, the initiated output pulse will last for a period of timedetermined by the circuit time constants and independent of the lengthof the applied impulses, 20, 2|, 22, etc. Accordingly, the outputcurrent from trig ger circuit !2 may be indicated by curve B of Fig. 2.It Will'be noted that the pulses 20A, ZIA, 22A and 23A are all initiatedat substantially the same time with respect to the corresponding pulses20, 2|, 22 and 23 and that they are all of equal dura tion, slightlygreater than the duration of the pulses. Likewise, the amplitude ofthese output pulses is independent of the input amplitude since it iscontrolled entirely by the constants of the trigger circuit and thevoltages 7 to a constant level before application to the triggercircuit. Furthermore, it is not necessary to firstdetectthe radiofrequency pulses to envelope frequency before application to themulti-vibrator circuit since the multi-vibrator itself performsthefunction of detecting the signals and is triggered by them for thefinal signal reproduction.

The trigger circuit of Fig.3 has been described as an element of thereceiver system of Fig. 1. It may,'however, be used in otherconnections. By adding a tuned circuit, Fig. 4, tothe output line asindicated at line 4-4 the circuit mayoperate as a frequency changer toconvert the received radio frequency pulses to damped wavetrain pulsesof a different radio frequency with-,- out disturbing their timespacing. By selecting the values of inductance 10 and-condenser 'H- toany frequency which is a harmonic of the pulses produced in the outputof the multi-vibratorim-v pulses of thisharmonic frequency having anamplitude and duration determinedby thejoutput impulsesof the trig ercircuit may be produced. These waves may; then be passed to anytranslating apparatus ,12 for further operation as desired.,

Generally, the direct current impulses in the output of the triggercircuit will not contain frequency components higher than the initiatingra-' when the constants of and H are properly chosen the trigger circuitmay be used to produce reshaped output at the same radio frequency asthe initiating pulses if desired.

It is clear that many other known forms of trigger circuits may be usedin place of the particular circuit shown in Fig. 3. For example, anytype of multi-vibrator circuit may be used so long as it is properlybiased and is provided with a suitable tuned input circuit to developthe necessary operating voltage directly from the radio frequencyimpulses. It is further clear that an amplifier such as shown at I I isonly necessary in order that the amplitude of the received impulses beincreased. Even if no amplifier is provided, the trigger circuit willoperate providing the received pulses are of sufiiciently greatamplitude themselves.

While the trigger circuit of my invention is particularly useful inreceivers for time modulated impulse systems or for converting thereceived radio frequency, it is clear that the rinciples of my inventionare not limited to this particular combination. The trigger circuit maybe useful in obstacle detection systems for reshaping the refiectedimpulses prior to applying them to the control electrodes of anindicator. Furthermore, in accordance with my invention, the triggercircuit disclosed may be used in any case where it is desired to producedirect current pulses corresponding in space to alternating currentimpulses but independent of these pulses in amplitude and duration.

Many modifications of my invention will occur to those skilled in theart and the particular examples described are not to be considered aslimitations on the scope of my invention but merely as an illustrationthereof.

What is claimed is:

1. A circuit for producing output direct current pulses of predeterminedcharacter in response to applied radio frequency pulses of a givenduration comprising a trigger circuit for producing a pulse ofpredetermined duration at least as great as said given duration inresponse to applications to said circuit of a predetermined voltage, aninput circuit for said trigger circuit comprising a tuned circuitresonant to the radio frequency of said radio frequency pulses fordeveloping said predetermined voltage to cause operation of said triggercircuit, and an output circuit for said trigger circuit for derivingtherefrom the produced direct current pulses.

2. A circuit according to claim 1, further comprising a circuit tuned toa predetermined radio frequency component of said direct current pulsescoupled to said output circuit whereby radio frequency pulses whoseduration is independent of said applied radio frequency pulses areobtained.

3. A radio receiver for time modulated pulse reception, comprising areceiving amplifying means for amplifying a succession of receivedpulses of a given radio frequency, a circuit for detecting saidamplified radio frequency pulses and shaping the resultant detectedpulses, said circuit comprising an input circuit tuned to said radiofrequency for developing a predetermined voltage, a trigger circuitnormally in unoperated condition and operative into operated conditionin response to said predetermined voltage, means for coupling said tunedcircuit to said trigger circuit, and time constant means for maintainingsaid trigger circuit operated for a substantially constant period oftime at least as great as the duration time of said amplified pulses,means cou- I pled to the output of said circuit for deriving a 4. Aradio receiver according to claim 3 where"- in said circuit furthercomprises means for determining operation of said trigger circuit to apredetermined amplitude, to control the amplitude level of said directcurrent pulses to substantially a constant value independent of saidapplied pulses. I

5. A radio receiver for time modulated pulse translation, comprising areceiving amplifying means for amplifying a succession of receivedpulses of a given radio frequency, a circuit for detecting and shapingthe detected envelope of said amplified radio frequency pulses, saidcircuit comprising an input circuit tuned to said radio frequency fordeveloping a predetermined voltage, a trigger circuit normally inunoperated condition and operative into operated condition in responseto said predetermined voltage, means for coupling said tuned circuit tosaid trigger circuit and means for maintaining said trigger circuitoperated for a substantially constant period of time at least as greatas the duration time of said amplified pulses, means coupled to theoutputof said circuit for deriving a direct current pulse in response toeach operation of said circuit, and means tuned to a fixed radiofrequency which is a component of said direct current pulses forderiving reshaped time modulated pulses from said direct current pulses.

6. A circuit for detecting radio frequency input pulses and producingtherefrom output pulses having substantially the same timed relation toone another as the input pulsesand amplitudes and duration periodsindependent of those of the input pulses, comprising an impulse triggercircuit having an input circuit and an output circuit, means normallymaintaining said trigger circuit in unoperated condition, meansresponsive to a predetermined input voltage for rendering said triggercircuit operative, duration I control means for maintaining said triggeron cuit operative for a predetermined interval after application of saidpredetermined voltage, means in said input circuit resonant to saidradio frequency for receiving said radio frequency pulses and developingsaid predetermined voltage in response to each said received pulses tocause operation of said trigger circuit, and means in the output circuitof said trigger circuit for deriving pulses of predetermined amplitudeand duration in response to operation of said trigger circuit.

DONALD D. GRIEG.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Garceau Dec. 1 1942

